1. Field of the Invention
Improvements in the manufacturing of high technology items such as micro-electronic devices have necessitated the maintenance of essentially a clean room atmosphere. These devices are, in essence, micro processors, the equivalent of the central processing unit of a small computer. They are manufactured using "wafers", thin slices of silicone on which circuits have been fabricated. The integrated circuits accomplish the separation and interconnection of transistors and other circuit elements electrically. The circuit elements are interconnected by a conducting film of evaporated metal that is photoengraved to leave the appropriate pattern of connections. An insulating layer is required to separate the underlying semiconductor from the metal film except where contact is desired. This insulating layer is formed on the surface of the wafer after the wafer has been processed and before the conducting metal is evaporated on it. Contamination, even by bits of lint or dust can bridge these circuits and cause such devices to be defective and is a major source of rejection. Therefore, there is a need to maintain all surfaces and workpieces as free from such contamination as possible. This is usually accomplished in part by wiping these surfaces, and a number of specialized wipers have been developed for this purpose. However, it is critical that the wiper, itself, in addition to being able to wipe cleanly, not contribute to the problem of dusting or linting. Conventional cloth wipes and tissue wipes, accordingly, are not entirely satisfactory. Various nonwoven wipes are also available, but while some are low linting, these require treatment for wettability in order to provide the absorbency and clean wiping characteristics desired for these applications. Such treatments have been most effective utilizing an anionic wetting agent such as Aerosol OT which is high in sodium ion content. These metallic ions present special problems since, if present in high enough concentrations, they may change the electrical properties of metal oxide semiconductors making the devices defective. Accordingly, such wipers have also not been entirely satisfactory. A need, therefore, has been demonstrated for a low linting, clean wiping wiper low in metallic ion content for these specialty applications and for other applications as well.
2. Description of the Prior Art
As stated above, nonwoven disposable and limited use wipers are well-known. Any of a number of nonwoven processes can be used to form base materials for wipers. For example, nonwovens formed by meltblowing, spinning, carding, and fibrillating techniques have been utilized. When formed from synthetic thermoplastic filaments, such materials are normally hydrophobic and non-wettable. For most applications, therefore, it is necessary to treat the nonwoven to make it wettable. A wide variety of anionic and nonionic wetting agents has been developed for this purpose and are in use. Among these, sodium dioctyl sulfosuccinate, such as Aerosol OT, has become a highly preferred agent as providing rapid wettability. For less demanding applications, other wetting agents such as those identified below have been used.
For clean room applications such nonwoven wipers have not proven entirely satisfactory because the treatments for wettability have required a compromise between wetting characteristics produced by Aerosol OT and the need for low metallic ion content. Other specialty wipers have been developed for these applications. For example, woven textile wipers have been used but are expensive and linty. Long fibered, wetlaid cellulose wipers tend also to be linty and of low absorbency and bulk.
Representative descriptions of the prior art products and materials include U.S. Pat. No. 3,811,957 dated May 21, 1974 to Buntin which describes meltblown materials and wettability treatments, U.S. Pat. No. 2,999,265 dated Sept. 12, 1961 to Duane et al. directed to a cleansing and deodorizing pad having a surface active agent treatment, U.S. Pat. No. 3,520,016 dated Oct. 9, 1968 to Meitner describing a cellulosic wipe, U.S. Pat. No. 3,954,642 and 3,956,155 dated May 4 and May 11 1976, respectively, to Schwuger describing textile wipes, and U.S. Pat. No. 3,978,185 dated Aug. 31, 1976 to Buntin et al describing a meltblown material useful as a wiper.